Power consumption greatly fluctuates depending on a season and a time zone. For example, power consumption is maximized in summer (from July to September) in which power consumption for air conditioning increases in a year. Moreover, power consumption is maximized in the time zone from 1:00 to 4:00 PM. That is, a power consumption peak lies in a time zone from 1:00 to 4:00 PM in summer (from July to September).
An electric power company sets a power generation capacity on the basis of the power-consumption peak. However, the power generation capacity is surplus except the peak period. In Japan, the load factor to the total power generation capacity averaged through a year ranges between 50 and 60% and the remaining 40 to 50% correspond to the peak period of power consumption. Therefore, it can be said that a sufficient power generation capacity is prepared. Here, the load factor denotes the ratio of annual average power consumption to peak power consumption. To consistently supply power at a low cost, it is preferable that the load factor remain high, often, however, in practice, the load factor tends to lower and the peak demand of power tends to sharpen.
From the above, various apparatuses for shifting the peak period of power consumption (peak shift) or correcting the power consumption peak (peak cut) have been proposed in order to improve a load factor.
For example, one such apparatus is a heat storing air conditioning system. The heat storing air conditioning system produces ice and stores cold heat in the nighttime when power consumption is small and performs the cooling operation in the daytime by using cold heat. More specifically, it has been proposed to perform the cooling operation (peak cut) between 1:00 and 4:00 PM. only by the cold heat stored in the nighttime and perform the combined cooling operation (peak shift) using the cold heat together in a period other than the period between 1:00 and 4:00 PM.
Moreover, it is also known to spread the power source such as in an ECO VENDOR design, for the peak cut period. The ECO VENDOR is a vending machine provided with a peak cut function of automatically stopping a cooling power source in a power consumption peak time zone in summer in order to control the power consumption in the time zone. Moreover, at a domestic level, a home distribution board provided with the peak cut function has been proposed. Some of home distribution boards have a function of monitoring home power consumption, notifying a person of any increase in power consumption by a sound or the like, and turning off a selected power source when power is still consumed.
As described above, under the circumstance in which a load factor lowers, an apparatus provided with the peak shift function or peak cut function (these are hereafter generally referred to as peak shift) plays an important role.
The heat storing airs conditioning system and ECO VENDOR are both apparatuses providing a cooling function. It is therefore desirable to provide the peak shift function of apparatuses that consume power from the viewpoint of environmental problems. It is necessary to note that it is desirable to preserve the essential function of the apparatus concerned, which in general would likely also deteriorate by using the peak shift function. For example, in the case of the ECO VENDOR it is not preferable that a refreshing drink product to be sold be insufficiently cooled by automatically stopping a cooling power source.